Nanoparticles of ultrafine particles down to nanometer (10−9 m) ranges from substances can produce various unique properties which are not provided by any bulk material, and thus have been attracting particular attention in combination with dramatic progress of nanostructure evaluation technology.
Among the foregoing nanostructures, thin-film structural bodies that have phase-separated nanostructures of separate phases dispersed in matrix phases have also been actively studied, for use as novel functional materials.
For example, Non-Patent Document 1 reports therein strain control and a spontaneously formed phase order in heteroepitaxial thin films of vertical nanostructures.
According to Non-Patent Document 1, with the use of a mixture of La0.7Sr0.3MnO3 (LSMO) and ZnO, heteroepitaxial growth by self-organization is induced on a SrTiO3 substrate, thereby forming a thin film that has a phase-separated nanostructure of ZnO as a matrix phase and LSMO as a columnar separate phase. Likewise, a fixture of BiFeO3 and Sm2O3 is used to form a thin film of Sm2O3 as a matrix phase and BiFeO3 as a separate phase on a SrTiO3 substrate.
More specifically, according to Non-Patent Document 1, the spontaneous formation of phase orders with the use of the magnetic materials provides heteroepitaxial films of vertical nanostructures on the SrTiO3 substrates. Non-Patent Document 1 discusses therein interface strain at the junction interfaces between the matrix phases and the separate phases, and reports that vertical strain is controlled by the strain state in a thin film in excess of 20 nm in thickness.
In addition, Non-Patent Document 2 reports a self-organization single-crystal ferromagnetic iron nanowire formed by decomposition.
According to Non-Patent Document 2, with the use of La0.5Sr0.5FeO3 as a target substance, the target substance is irradiated with a pulsed laser while heating a single crystal SrTiO3 (001) substrate to 760° C. under high vacuum, thereby decomposing La0.5Sr0.5FeO3 into LaSrFeO4 and Fe, and thus providing a nanostructure that has a self-organized vertical α-Fe nanowire embedded in a LaSrFeO4 matrix.
Further, Non-Patent Document 2 reports therein that the prepared α-Fe nanowire has strong magnetic anisotropy, and differs in magnetic property depending on the growth orientation of epitaxial film.
On the other hand, in recent years, from the perspective of reduction of global environmental burden, attempts to use natural energy have been also actively made, and in combination with the progress of semiconductor technology, solar cells have been also actively researched and developed with the use of the semiconductor technology.
For example, Non-Patent Document 3 reports therein the preparation of a visible-light transmission solar cell with the use of a p-type NiO film obtained by a low-oxygen partial pressure reactive RF sputtering deposition method.
According to Non-Patent Document 3, under an extremely low oxygen partial pressure at which the proportion of O2 to the total of Ar and O2 is 0.5%, the p-type NiO film with a light transmission in excess of 80% in the wavelength range of 500 to 800 nm is obtained by the reactive RF sputtering. Further, it is reported therein that when an n-type ZnO layer was stacked on the p-type NiO layer to prepare a solar cell with a p-n junction, a clear photoelectric effect was observed, although the effect was slight.    Non-Patent Document 1: J. L. MacManus-Driscoll et al., “Strain control and spontaneous phase ordering in vertical nanocomposite heteroepitaxial thin film”, Nature Material, Vol. 7, April 2008, pp. 314-320    Non-Patent Document 2: L. Mohaddes-Ardabili et al., “Self-assembled single-crystal ferromagnetic iron nanowires formed by decomposition”, Nature Material, Vol. 3, August 2004, pp. 533-538    Non-Patent Document 3: M. Warasawa et al., “Fabrication of Visible-Light-Transport Solar Cells Using p-Type NiO Films by Low Oxygen Fraction Reactive RF Sputtering Deposition”, Japanese Journal of Applied Physics, 52 (2013), pp. 021102-1-021102-4